The anti-lock brake system (ABS) is designed to detect the occurrence of tires being locked during run on a low friction road surface or at the time of panicked braking so that the braking can be relieved to secure a tire grip to improve the maneuvering stability. An ABS sensor for detecting the occurrence of the tire being locked is incorporated in a wheel support bearing assembly.
As such a passive type ABS sensor used in the wheel support bearing assembly, an annular type rotation sensor has been suggested (See, for example, the JP Laid-open Patent Publications No. 5-264562 and No. 8-285879.). This annular type rotation sensor includes a magnetic encoder having a multipolar magnet, and a magnetic sensor having a coil built therein in face-to-face relation with the multipolar magnet and is so operable that when magnetic fluxes passing the magnetic sensor as a result of rotation of the magnetic encoder change, an electric voltage can be induced across the coil to detect the rotation of a vehicle wheel.
Also, as shown in FIG. 10, it is suggested that the magnetic sensor 36 of the structure described above is resin molded together with a connector pin 43 to form a generally cylindrical sensor connector 42, which is in turn press-fitted into a generally cylindrical sensor cap 32 having a bottom surface. This is so designed that as shown in FIG. 11, when the sensor connector 42 is incorporated in the sensor cap 32 and the sensor cap 32 is then press-fitted into a stationary raceway member of the wheel support bearing assembly, the magnetic sensor 36 can be fixed in position in the stationary raceway member through the sensor cap 32. In such case, the magnetic encoder is fixed on a rotatable raceway member of the wheel support bearing assembly in face-to-face relation with the magnetic sensor 36.
In addition, as the wheel support bearing assembly having the rotation sensor built therein, what is shown in FIG. 12 is also available (See, for example, the JP Laid-open Patent Publication No. 9-329611.).
This wheel support bearing assembly with the rotation sensor includes an outer member 60 having an inner periphery formed with double rows of outer raceway surfaces 60a and 60a and serving as a stationary member, an inner member 50 having an outer periphery formed with double rows of inner raceway surfaces 51a and 52a opposed respectively to the outer raceway surfaces 60a and 60a and serving as a rotatable raceway member, double rows of rolling elements (balls) 61 rotatably interposed between the raceway surfaces 60a and 51a and between the raceway surfaces 60a and 52a, an annular tone wheel or encoder wheel 62 fixed on the inner member 50 and having characteristics alternately and equidistantly changing in a circumferential direction thereof, a cover 63 fixed to an inboard open end of the outer member 60, an annular rotation sensor 64 opposed to the tone wheel 62, and a sensor cap 65 fixed to a peripheral surface of an open end of the cover 63. The cover 63 is fixed to the outer member 60 with one peripheral surface of the sensor cap 65 press-fitted into an outer peripheral surface of one end of the outer member 60.
The inner member 50 has one end formed integrally with a wheel mounting flange 53 for the support of a vehicle wheel (not shown) and is made up of a hub axle 51 formed with the inner raceway surface 51a on the outer periphery thereof and a reduced diameter stepped portion 51b axially extending from the inner raceway surface 51a, and an inner race 52 mounted on the reduced diameter stepped portion 51b and formed with the inner raceway surface 52a on the outer periphery thereof.
The cover 63 is made up of a sensor connector 66 made of a synthetic resin and the sensor cap 65 made of a metallic material, and the sensor connector 66 includes a disc portion 66a and a cylindrical portion 66b extending axially from the disc portion 66a. The rotation sensor 64 formed to represent an annular shape is supported embedded on an outer surface side of the disc portion 66a. The cylindrical portion 66b has a free end formed with a recessed groove 67 that extends over the entire circumference thereof and is defined between an large diameter portion 65a and a stepped portion 65b of the sensor cap 65, and a seal ring such as an O-ring 69 is engaged inside the recessed groove 67. In this construction, the cover 63 can be removably mounted on the outer member 60 without impairing the sensor connector 66 made of the synthetic resin and forming a part of the cover 63 while preventing water from flowing into the outer member 60.
However, in the structure shown in FIGS. 10 and 11, the sensor connector 42 has an outer periphery press-fitted into the inner periphery of the sensor cap 32 with a predetermined allowance therebetween and the end of the sensor connector 42 is held in abutment with a bottom surface of the sensor cap 32 to complete assemblage of the sensor connector 42 with the sensor cap 32. Because of this, depending on the diametric dimension of the outer periphery of the sensor connector 42 and/or the diametric dimension of the inner periphery of the sensor cap 32, the press-fitting allowance varies considerably and, as a result, a press-fitting load changes, resulting in difficulty in assemblage.
Also, the sensor connector 42 is axially positioned relative to the sensor cap 32 by abutting the end of the sensor connector 42 with the bottom surface of the sensor cap 32 and, therefore, when the necessity arises to perform a fine adjustment of the axial position of the sensor connector 42 in order to increase the accuracy of an output signal of the rotation sensor 64, it often occurs that the fine adjustment to be carried out by pressing the sensor connector 42 deep into the sensor cap 32 cannot be performed easily.
On the other hand, in the rotation sensor incorporated wheel support bearing assembly shown in FIG. 12, a mounting gap of 20 to 100 μm is present between a knuckle N, forming a part of the suspension system, and a pilot portion 68 of the outer member 60 (which is the large diameter portion 65a of the sensor cap 65 in the instance shown) and, therefore, there is a high possibility that salty water and/or dusts may ingress into the gap and rusting may eventually occur accordingly. Once the pilot portion 68 rusts, removal of the outer member 60 from the knuckle N would be difficult to achieve.
In addition, in view of the fact that the seal ring such as the O-ring 69 is engaged in the recessed groove 67 formed in the free end of the cylindrical portion 66b of the sensor connector 66 forming a part of the cover 63, it is possible to avoid an ingress of water inside the outer member 60, but there is the risk that once the pilot portion 68 rusts, the cover 63 is axially displaced by the effect of a volume expansion of the rust, resulting in a disorder of the positional relation between the rotation sensor 64 and the tone wheel 62. Once this positional relation disorders, the accuracy of the output signal of the rotation sensor 64 is impaired and depending on a situation the output signal will fail to emerge.